In industry there are many instances where "temperature alert" signals are needed. In many cases, when a temperature reaches above or below a certain value or a set range, this change must be observed and a response made. This often occurs in operation of chemical processes, in storage of packaged temperature-sensitive products, and the like. Moreover, there are many instances where it is simply impractical to have sophisticated electrical sensors, either because such devices are too expensive or because of the skill needed for their operation and maintenance.
There is therefore a real and continuing need for the development of thermochromic materials, which can change color as the temperature changes. They are similar to the litmus paper, used for testing the acidity or basicity of solutions. Moreover, there is also a continuing need for the development of thermochromic materials whose color is responsive over a wide range of pH, regardless of the other ions present in the medium.
An ideal thermochromic material is one whose color changes abruptly, rather than gradually, so that a sudden change is immediately apparent to observers who are monitoring temperature. An ideal thermochromic material is also one whose concentration can be varied in order to adjust the threshold temperature, at which the color changes. In the ideal case, the variables affecting the temperature threshold can be controlled. Here, this "alert temperature" can be varied by simply varying the concentration.
A yet further characteristic of an ideal thermochromatic material is that it undergoes not only a color change, but also a phase change. Thus, observers who are monitoring the temperature to determine change can immediately see not only color, but also phase change. Finally, the changes in color and phase should occur suddenly and dramatically for easy notice.
The primary objective of the present invention is to provide a thermochromic material that is closer to the ideal material than those used before, in the sense that the "alert temperature" can be varied by simply manipulating the concentration of the thermochromatic material.
A yet further objective of the present invention is to provide a thermochromic material which not only has color change based upon sensing of temperature, but which also has phase change.
A still further objective of the present invention is to provide a thermochromic material which is easy to prepare, and which provides dramatic, sudden, and reversible color and phase changes.
The method and manner of accomplishing each of these objectives as well as others will become apparent from the detailed description of the invention which follows hereinafter.